1. Technical Field of the Invention
This invention relates to radio telecommunication systems and, more particularly, to a Packet Core Function (PCF) and method of selecting a Packet Data Service Node (PDSN)/Foreign Agent (FA) in a packet data network.
2. Description of Related Art
Code Division Multiple Access (CDMA) 2000 is the third generation system for CDMA networks. It offers packet-switched call routing via Packet Data Service Nodes (PDSNs) which are used as access concentrators and, in the case of Mobile IP, as Foreign Agents (FAs) for roaming mobile subscribers.
FIG. 1 is a simplified block diagram of an existing packet data network 10 providing radio access to a plurality of mobile subscribers utilizing Mobile Nodes (MNs) 11-13. In packet data networks such as CDMA 2000, MNs gain access to the packet core network through Radio Networks (RNs) 14 and 15 over an air interface link 16. An illustration a of the protocols utilized, and where each protocol ends, is shown below the block diagram. An Internet Protocol (EP) network 17 links the RNs to a plurality of PDSNs 18-20 using a Radio-Packet (R-P) interface 21. Each RN may include a plurality of Base Stations (BSs) and Base Station Controllers (BSCs) (not shown). Packet Core Functions (PCFs) 22 and 23 handle the switching of data packets that come from the MNs, and may be located in the BSCs. The PCF selects one PDSN to terminate all of its packet data sessions. When a mobile subscriber desires to initiate a packet data session, the PCF selects a PDSN, and a Point-to-Point Protocol (PPP) connection 24 is established between the subscriber""s MN and the selected PDSN. Each time a PPP link is established, negotiation takes place with regards to authentication, compression, etc., followed by Agent advertisement and a Mobile IP registration request.
The PDSNs, in turn, utilize one or more sub-networks 25 and 26, and routers 27 and 28 to access the packet-switched network backbone 29. At that point, the MN is connected to the IP network 17, and the IP protocol 30 may be utilized to access the Internet.
The CDMA 2000 standard describes two possible subscription types for mobile subscribers: xe2x80x9cSimple IPxe2x80x9d and xe2x80x9cMobile IPxe2x80x9d. In Simple IP, seamless mobility between different PDSNs is not feasible. For a particular data session, the. IP address for a mobile subscriber""s MN is provided by the PDSN handling that particular session. Therefore, the MN cannot be handed over to another PDSN while continuing a data session because the new PDSN would assign a new IP address to the MN. If the MN receives packets with a new IP address, it automatically concludes that the first session has ended. Therefore, if an MN roams from one PDSN to another in Simple IP, the entire session must be re-negotiated from the beginning. This may involve allocation of traffic channels which should be avoided in the event of dormancy, as well as an entire series of protocols in order to reestablish the session. This process could be long enough to be a visible problem to the user.
In Mobile IP, on the other hand, each MN is pre-allocated an IP address that it always uses regardless of the serving PDSN. A Mobile IP protocol layer on top of the IP layer permits a home agent and a foreign agent to tunnel data towards roaming Mobile IP subscribers. Therefore, during a handover, the new PDSN uses the same pre-allocated IP address as was being used by the old PDSN. However, if the MN keeps switching from one PDSN to another, additional allocations of traffic channels are required, which is an inefficient usage of the air interface.
Mobile IP service is currently described in the CDMA 2000 packet data standard IS-835. The existing standard, however, does not effectively describe any methodology by which an MN may consistently select the same PDSN from a packet data network in order to set up its communication links. The standard makes the assumption that when the PCF is selecting a PDSN, the PCF will be able to select the PDSN with which it has a previous PPP connection. However, with the current PDSN-selection procedures, the selection of the same PDSN is not always assured. This issue is important for both Mobile IP users (provided the PPP and the Mobile IP bindings are still active) and Simple IP users, but is particularly critical for Simple IP users where it is even more critical to maintain the connectivity with the same PDSN.
Thus, it would be advantageous for an MN to be able to consistently select the same PDSN for access to the packet data network because this would enable the PPP session between the MN and the PDSN to be preserved. Other proposed solutions to this problem involve methodologies that are performed within the packet core network. These proposals have a centralized view of the network, and require additional network nodes and additional network signaling in order to communicate with or update the configuration of the PDSN and all the current connections that are being set up. It would be preferable to have a solution that is performed in the radio network and does not involve additional nodes or signaling in the core network.
Dormant handoffs are also a problem under the existing standards. In CDMA 2000, the MN goes dormant when no data is transferred over the link for a certain period of time. During the dormant stage, there is no traffic channel assigned to the mobile station; however, the PPP session is maintained. When the dormant MN moves from one packet cell to another, the MN notifies the access network, and the PCF within the access network attempts to select a PDSN for the MN. It would be desirable to select the same PDSN where the PPP and RP connections are still maintained for the Mobile IP user. Otherwise, the network may unnecessarily maintain multiple xe2x80x9changing PPP connectionsxe2x80x9d in more than one PDSN until the original PPP connections time out and are released. Since PPP resources are expensive to the operator, this is an expensive waste of network resources.
In order to overcome the disadvantage of existing solutions, it would be advantageous to have a method that enables a PCF to consistently select the same PDSN. The method should preferably be a simple selection process that is performed primarily in the radio network, and that does not require the introduction of new nodes or new signaling in the core network to handle the functionality. The present invention provides such a method.
In one aspect, the present invention is a method of consistently selecting a particular PDSN from a plurality of PDSNs in a packet data network to host a data session for an MN. The method begins by storing a static lookup table in a PCF, the table including a list of identifiers for MNs and an associated list of the plurality of PDSNs in the network. The PCF then obtains an identifier for the MN and utilizes the lookup table to associate the identifier for the MN with a PDSN. The PDSN is then selected by the PCF to host the data session for the MN. The lookup table is preferably stored in every PCF in the network so that the same PDSN is consistently selected for the MN as it roams in different PCFs.
In another aspect, the present invention is a method of reselecting a particular PDSN from a plurality of PDSNs in a packet data network to host a data session for an MN following a handoff of the MN from a source PCF to a target PCF when the MN returns to the source PCF. The source PCF initially assigned the PDSN to host the data session before handing off the MN. The method includes the steps of storing in a cache memory in the source PCF, an identifier for the MN and an IP address for the particular PDSN for a predetermined period of time after handing off the MN. If the MN returns to the source PCF within the predetermined period of time, the PCF reselects the particular PDSN to host the data session.
In yet another aspect, the present invention is a method of consistently selecting a particular PDSN from a plurality of PDSNs in a packet data network to host a data session for an MN. When a PDSN is initially selected to host the data session, the IP address of the PDSN is sent to the MN where it is stored. Thereafter, when the MN roams to another PCF, the MN passes the IP address of the PDSN to the new PCF using, for example, CDMA 2000 air interface layer 3 signaling.
In another aspect, the present invention is a PCF that consistently selects a particular PDSN from a plurality of PDSNs in a packet data network to host a data session for an MN. The PCF includes a static lookup table that includes a list of identifiers for MNs and an associated list of the plurality of PDSNs in the network. The PCF also includes means for obtaining an identifier for the MN, and a hash function that associates the identifier for the MN with the particular PDSN utilizing the lookup table, and selects the particular PDSN to host the data session for the MN. The PCF may also include a cache memory that stores the identifier for the MN and an IP address for the particular PDSN for a predetermined period of time after handing off the MN to another PCF. A cache timer determines whether the predetermined time period has expired, and the PCP reselects the particular PDSN to host the data session if the MN returns to the PCF within the predetermined period of time.
In yet another aspect, the present invention is a system for consistently selecting a particular PDSN from a plurality of PDSNs in a packet data network to host a data session for an MN. The system includes a Radio-Packet (R-P) network that connects each of a plurality of PCFs to the plurality of PDSNs. Each PCF selects a PDSN to host the data session when the MN roams into an area controlled by the PCF. Each of the PCFs includes a lookup table for associating MNs with PDSNs in the network, means for obtaining an identifier for the MN, and a hash function that associates the identifier for the MN with the particular PDSN utilizing the lookup table, and selects the particular PDSN to host the data session for the MN.